This invention relates to cable junctions or terminations for subsea use as on offshore oil platforms or other subsea projects. More particularly, the invention relates to such junction or termination boxes which are configured to be pressure balanced internally with respect to a subsea environment at any subsea depth at which such cables are designed for use.
In the operation of offshore oil platforms it is often necessary to install electrical power or communication cables across or immersed in bodies of fresh, saline or salt water. Such cables are typically comprised of several jacketed conductors, filler layers between the conductors, an outer jacket layer and a protective armor layer for load bearing applied over the entire cable structure. When terminating such cables, or joining them, beneath the surfaces of the water it is common practice to use cable termination boxes or cable junction boxes to prevent water leakage into the internal cable structure at the termination or joint and to provide a load bearing structure coupled to the cable armor for handling the cable by lifting or placing machinery.
In the case of power cables in particular, water leakage to the cable interior can cause severe problems such as short circuits and the like. Previous attempts to seal, exteriorly to a cable junction box or termination box, all of the orifices and seams have often proved to be unsuccessful in preventing water intrusion when the cable junction or termination box is used in, say, 100 ft. of water or the like. At 100 ft. depth approximately three atmospheres of pressure exists in the water. Inside a cable box sealed at the surface an insulating fluid or air is present at one atmosphere of pressure. The lower pressure drop inside cable and the box can cause entry of water through faulty seals or by migration along the cables itself, either between the armor layer and the outside cable jacket, or in the cable interstices themselves if the filler material is permeable in nature as is the case in typical power cables.